SmC Mesophase Research Articles

Biphenyl Benzoate Derived Polymorphic Self-Assembling Chalcones: Influence of Mesogenic Core Variations And Terminal Alkyl Chains

The construction of multifunctional molecular self-assembly is one of the fascinating areas of current research. Herein we reported a series of biphenyl benzoate derived mesogenic material EBPCH-(2–16), containing ester-imine and chalcone as connecting units. Compounds were substituted by decyloxy chain at one end while the other end has been systematically varied from C2-C16. By using various spectroscopic techniques, and elemental analysis, the structures of the biphenyl benzoates were determined; the results are consistent with the suggested structure. The mesomorphism of new molecules has been studied by differential scanning calorimetry and polarizing optical microscopy. Initial members of the series up to C8 exhibited enantiotropic Smectic-A (SmA) as well as nematic mesophase with good thermal stability, whereas compounds above C10 up to C16 revealed only smectogenic behaviour with enantiotropic SmA as well as SmC mesophase. Apart from these findings, additional variables like the alkyloxy groups in the molecules and the polarity and polarizability of the linking units may also have an impact on these mesogens. Further, the structure–property relationship was carried out by thorough investigations and comparison with structurally related literature on the target compounds’ mesomorphism. In addition, Density functional theory simulations verify the potential conformer of biphenyl benzoates, whereas studies conducted by frontier molecular orbitals and molecular electrostatic potential delve into the molecular surroundings and quantum chemical behaviour of these compounds.

Comments on the dielectric spectroscopy results on a new series of fluorinated hydrogen-bonded liquid crystals

Recently, a work entitled “Synthesis, thermal, dielectric and electro-optic properties of new series of fluorinated hydrogen-bonded liquid crystals” is published by M. Derbali et al., in J Mol Liq, 367 (2022) 120510. Authors reported SmA and SmC mesophases in the synthesised liquid crystalline materials. However, dielectric data reported here are erroneous when tested even from some fundamental aspects. Inadvertent omissions by the authors in presenting and explaining the dielectric results in terms of frequency dependent permittivity and loss are discussed here so that appropriate precautions may be taken by the readers to avoid such fundamental gross mistakes. Some problems related to other studies are also discussed in brief.

Preparation and properties of novel liquid crystal ionomers bearing benzoxazole-based mesogenic side-chains and their membranes

A new heterocyclic mesogenic compound, 6-[4-(5-chloro-2-benzoxazolyl)phenoxy]-hexanethiol (CBPHT), is designed and synthesized, which shows an enantiotropic SmC mesophase with the liquid crystal phase ranges of 5.67 °C and 22.99 °C on heating and cooling, respectively. The CBPHT-based side-chain liquid crystal polymers (LCP-x) are obtained via a nucleophilic substitution between CBPHT and polyepichlorohydrin, and also shows an enantiotropic SmC mesophase with narrow temperature range. Furthermore, novel side-chain liquid crystal ionomers (LCI-x) with enantiotropic SmC mesophase are prepared via quaternization of N-methylimidazole with LCP-x, where polyepichlorohydrin, CBPHT and methylimidazolium chloride act as polymer main-chain, mesogenic side-chain, and ionic group, respectively. In addition, LCI-x membranes can be fabricated via a solution casting method, and exhibit high thermal stability, good mechanical properties and high ion conductivity. For example, LCI-0.20 with a low ion exchange capacity of 0.12 mequiv. g−1 has a large elongation at break (385 %) and a high chloride ion conductivity (20.68 mS cm−1), indicating a high potential for application as polymer electrolyte membrane.

Design of unsymmetric coumarin chalcone derivatives with tunable self-assembling behavior

Unsymmetric coumarin chalcone derivatives were designed with unsymmetric alkoxy chain on both terminal of the molecules to find their effect on the overall mesomorphic properties. In the first homologous series, compounds with fixed octyloxy chain on chalcone end and varied alkoxy chain length at coumarin end of the molecule (n = 10,12,14,16,18) have been analyzed for their mesomorphic properties. In this series, all the Compounds showed stable enantiotropic SmC mesophase. In the second homologous series, compounds with fixed octyloxy chain on coumarin end and varied alkoxy chain length at chalcone end (n = 10,12,14,16,18) have been studied for their mesomorphic properties. In the second homologues series, compounds (n = 10,12) exhibited monotropic nematic mesophase. For higher analogues (n = 16,18), enantiotropic SmA mesophase was observed. Further, the powder X-ray diffraction analysis of the three compounds from both the series at 112 °C showed diffraction pattern quite close to identified mesophase type. To understand effect of variation of terminal chain, DFT theoretical study was carried out for both different series and tried to understand correlation between mesomorphic properties and structural parameters.

Synthesis and characterization of newly syringaldehyde based chalcone liquid crystals

In present study, two homologues series were synthesized based on chalconyl-ester and chalconyl-vinyl ester linking group. The mesomorphic properties of both calamitic-shaped homologues series were studied by polarized optical microscope and differential scanning calorimetry. In both series, SmC and nematic type mesophase pattern were observed with good temperature range and thermal stability. Further, the structure-property relationship has been studied for a better understanding about the effect of linking group on the mesogenic properties. The results indicate that the stability and type of the mesophase are dependent on the linking group with the addition of variable side alkoxy group on the terminal end group.

New Advanced Liquid Crystalline Materials Bearing Bis-Azomethine as Central Spacer.

In this study, a homologous series of novel liquid crystalline compounds bearing the bis-azomethine central linkage (–CH=N-N=CH–), namely ((1E,1′E)-hydrazine-1,2-diylidenebis(methanylylidene))bis(4,1-phenylene) dialkanoate (In), was synthesized, and the mesophase and thermal properties were investigated theoretically and experimentally. The molecular structures of the prepared compounds were determined using elemental analysis, NMR, and FT-IR spectroscopy. The mesophase transitions were detected by differential scanning calorimetry (DSC), and the mesophases were identified using polarized optical microscopy (POM). The results indicated that the derivative with the shortest length (I5) was purely nematogenic, while the other homologues (I9 and I15) possessed SmC mesophases. The optimal geometrical structures of the investigated group were derived theoretically. The estimated results demonstrated that all homologues were mesomorphic, and their type depended on the length of the terminal chains. Computations based on density functional theory (DFT) were used to explain the experimental data. The calculated dipole moment, polarizability, thermal energy, and molecular electrostatic potential all showed that it was possible to predict the mesophase type and stability, which varied according to the size of the molecule.

Solvent-Free Mechanochemical Synthesis of High Transition Biphenyltetracarboxydiimide Liquid Crystals.

A series of high temperature alkyl and alkoxy biphenyltetracarboxydiimide liquid crystals have been prepared under ball mill method using solvent-free mechanochemical approach. The thermal properties of the prepared compounds were investigated by deferential scanning calorimetry (DSC) measurements and the textures were identified by polarized optical microscope (POM). The compounds showed smectic mesomorphic behaviour. The results showed the increasing nature of transition temperature Cr-SmC with chain length with increments of the SmC mesophase range. However, the mesophase range of the SmA was decreased with the terminal chain length either for the alkyl or alkoxy terminal groups. Moreover, the DFT theoretical calculations have been conducted give a detailed projection of the structure of the prepared compounds. A conformational investigation of the biphenyl part has been studied. A deep illustration of the experimental mesomorphic behaviour has been discussed in terms of the calculated aspect ratio. A projection of the frontier molecular orbitals as well as molecular electrostatic potential has been studied to show the effect of the polarity of the terminal chains on the level and the gap of the FMOs and the distribution of electrostatic charges on the prepared molecules.

Liquid crystal behavior of Ag(I) complexes based on a series of mesogenic 1,3,4-thiadiazole ligands

2-(4-Alkoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazoles (alkoxy: O(CH2) n H, n = 1–8) ( 6a–h ) (as a series of 1,3,4-thiadiazole derivatives) and their silver(I) complexes: bis(2-(4-alkoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole)-silver(I) complexes (alkoxy: O(CH2) n H, n = 1–8) ( 7a–h ) were prepared and characterized with different techniques: microelemental analysis, FTIR, UV–Vis, 1H NMR, 13C NMR and mass (for the organic compounds) spectra, in addition to the molar conductivity measurements (for Ag(I) complexes). Liquid crystal behavior of the two series of compounds was evaluated using polarized light optical microscopy (POM). The study revealed that both series are enantiotropic liquid crystalline materials (exhibiting wide mesomorpic temperature ranges) with different behavior and properties. 6a–f displayed only nematic mesophase upon heating and cooling, while 6g and 6h exhibited both of SmC and nematic mesophases upon heating and cooling. Upon complexation of 1,3,4-thiadiazoles ( 6a–h ) to silver(I), the liquid crystal behavior and properties are significantly changed (different mesophases, and lower mesophase and clearing temperatures). However, 7b–h exhibited SmA mesophase upon heating and cooling, while 7a shows no mesomorphic properties (simply melted to isotropic liquid).

Luminescent mesogenic borondifluoride complexes with the Schiff bases containing salicylideneamines and β-enaminoketones core systems

Three new families of borondifluoride complexes 1a–c derived from salicylideneamines 2a and β-enaminoketonates 2b–c were reported, and their mesomorphic and optical properties were also investigated. One single crystal and molecular structure of nonmesogenic BF2 complex 1c (n=10) was resolved and the geometry of the central boron atom was tetrahedron. A larger dihedral angle of 81.3° between the two phenyl rings observed in crystal lattice was attributed to the lack of liquid crystallinity. Boron complexes 1a formed monotropic SmA phases, while boron complexes 1b exhibited enantiotropic SmC mesophases. The optical property of the boron complexes was dependent on their molecular structures, and they emitted a blue–to–green emission at λmax=476–541nm in the solution and 488–550nm in the solid state. This is the first group of mesogenic BF2 complexes with the Schiff bases derived from respective salicylideneamines and β-enaminoketones.

Mesomorphic properties of liquid crystalline compounds with chalconyl central linkage in two phenyl rings

ABSTRACTIn order to investigate the influence of the central linking group and the effect of flexibility on mesomorphism, we have synthesised a newly homologous series 3-(3-butoxyphenyl)-1-(4-n-alkoxy phenyl) prop-2-en-1-one (series-l) consisting of 13 homologues C1–C8, C10, C12, C14, C16 and C18. In the present series, mesophase commences from the C6 homologue. C1–C5 homologues did not exhibit liquid crystalline (LC) property, while C6–C12 homologues exhibited an enantiotropic nematic phase and the rest of the homologues C14–C18 displayed monotropic SmC and nematic mesophase. The transition temperatures of the synthesised compounds were determined by an optical polarising microscopy equipped with a heating stage. All newly synthesised compounds were confirmed by 1H-NMR, 13C-NMR, IR and elemental analysis.

Synthesis and characterisation of some new chalcone liquid crystals

ABSTRACTA series of new chalcones with four aromatic rings is synthesised and characterised. The chemical structures of chalcones are evaluated by Fourier transform-infrared spectroscopy, elemental analysis, 1H and 13C nuclear magnetic resonance spectroscopic techniques. The compounds were investigated for liquid crystalline properties using differential scanning calorimetry and polarising optical microscopy with hot stage. The results indicate that the formation of mesophase type is dependent on the alkyl chain length at one end of the molecule. Compounds 9a–d with relatively shorter chains show SmA and nematic mesophases, whereas 9e–g exhibit SmC and SmA mesophases. Compound 9h having a cyano group at one end, exhibit SmA and nematic mesophases.

Fluorescent mesogenic boron difluoride complexes derived from heterocyclic benzoxazoles.

One new series of boron difluoride complexes 1 derived from heterocyclic benzoxazoles 2 was reported, and their mesomorphic and optical properties were also investigated. One single crystal of the mesogenic BF2 complex 1a (m = 12, n = 8) was obtained, and its single crystal and molecular structure were resolved. The geometry coordination at the central boron atom is tetrahedral. It crystallizes in a triclinic space group P1[combining macron] with Z = 4. The overall molecular shape was described as slightly bent Z-shapes, and the molecular length was ca. 34.06 Å. Weak intramolecular and intermolecular H-bonds observed in the crystal lattice were attributed to the formation of mesophases. The results indicated that benzoxazoles 2a (n = 6, 8, 12) formed monotropic SmA phases, while boron difluoride complexes 1a (n = 6, 8, 12, 16) exhibited monotropic SmC mesophases. In contrast, all compounds of 2b and 1b (m = 1, n = 12 for all) were not mesogenic. Boron complexes 1 emitted a pronounced violet emission at λmax = 399 nm in solution at room temperature.

Lanthanide complexes of a mesogenic Schiff's base having 1,3,4-oxadiazole moiety: Synthesis and characterization

A liquid-crystalline Schiff's base (HL) having 1,3,4-oxadiazole moiety with an octyloxy substituent and a series of lanthanide(III) complexes [Ln(LH)3(NO3)3] (LnIII=La, Pr, Nd, Sm, Eu, Tb and Dy; HL=N-(4′-(5-(4″-octyloxyphenyl)-1,3,4-oxadiazol)-2-phenyl)-4‴-octyloxysalicylaldimine) have been synthesized and characterized by FTIR, 1H and 13C{1H} NMR, UV–Vis, fluorescence and Mass spectral techniques. HL exists in zwitter-ionic form in the complexes, binding to the metal through phenolate oxygen; Optical and thermal behavior studies (POM, powder XRD & DSC techniques) indicate SmC and SmX mesophases of HL and non-mesogenic behavior of the complexes.

An old dog with new tricks: Schiff bases for liquid crystals materials based on isoxazolines and isoxazoles.

AbstractSchiff bases are in action again showing an exuberant mesophase range despite their chemical and thermal weakness. Two series of Schiff bases (SB), based on isoxazolines 9 a–f and isoxazoles 10 a–f, are described. 9 a–f were synthesized by a [3+2] cycloaddition 1,3‐dipolar of arylnitrile oxide from p‐nitrobenzaldehyde (1) and alkenes. And, subsequently oxidized to 10 a–f by MnO2. The isoxazolines and isoxazoles thus obtained were reduced to aniline derivatives and condensed with appropriated arylaldehydes. The SBs series isoxazolines 9 a–f presented a narrow mesophase range, while SBs series isoxazoles 10 a–f showed a large mesophase range. Nematic mesophase was observed for SBs with short and non‐polar groups, while SmA and SmC mesophase for SBs with long and more polar terminal groups. The stability of the SBs is also dependent on the clearing temperature. For 10 a–f with high clearing temperature, decomposition induced by heat was observed during the first cycle of heating and in solutions of CDCl3. Series 9 a–f was more resistant to the thermal decomposition.

Microwave-assisted synthesis, characterisation and mesomorphic investigations of novel disubstituted aroylhydrazones

The present study is focused on the development of green microwave process for the synthesis of mesogenic substituted aroylhydrazones and their structure–mesophase relationship study. Two new liquid crystalline series of disubstituted aroylhydrazones with (ABB(OH)H-n) and without lateral hydroxyl group (ABBH-n) (n = 6–16) have been synthesised by microwave-assisted methods. The compounds were structurally characterised by using suitable spectroscopic techniques. The mesomorphic properties of the series of aroylhydrazones were examined using differential scanning calorimetric analysis and polarising optical microscopy. The relationship between structure and mesogenic properties was analysed by comparison of the present series and earlier reports on homostructural series of aroylhydrazones. Thus, the effects of substitution of phenyl rings with ester and ether linking group at both terminals and introduction of hydroxyl group at lateral position on stability of mesophase and their width were investigated. In general, all substituted aroylhydrazone derivatives exhibit SmC mesophase, and substitution of terminal and lateral group has considerably increased the stability and broadened the width of mesophase of the compounds.

Synthesis, Characterization And Mesomorphic Properties of Side Chain Liquid Crystalline Oligomer Having Schiff Base Type Mesogenic Group

A new liquid crystalline oligomer OLC was synthesized from its monomer having Schiff-base type mesogenic group MLC via free radical polymerization. The chemical structures of all compounds were confirmed using UV, FTIR, 1 H NMR, 13 C NMR and MS spectroscopy. Schiff-base type thermotropic system based on side chain oligomer containing long aliphatic branching was studied to determine the change in mesophase behaviour of the Schiff-base type mesogenic groups. A combination of differantial scanning calorimetry (DSC) and polarize optical microscopy (POM) demonstrated that the oligomer behaves similar to its monomer and both of them exhibit enantiotropic SmC and monotropic SmX mesophases. The oligomerization of the liquid crystal monomer gives rise to decreased transition temperatures whereas it has no influence on the type and stability of the mesophase formed. Namely, simply through oligomerization, we can greatly vary transition temperatures of the mesogenic groups.

Synthesis, characterization and mesomorphic investigations of ester-substituted aroylhydrazones possessing a lateral hydroxyl group

The synthesis, characterization and investigation of a new liquid crystalline series of ester containing aroylhydrazones with a lateral hydroxyl group, N-[4-(4′-alkoxy)benzoyloxy-2-hydroxy-benzylidene]-N′-[4″-alkoxybenzoyl]hydrazine (Cm,nLH), with the same or different peripheral alkoxy chains, and some of their nickel(II) and copper(II) complexes are described. All the ligands, except those with no terminal chains on either end of the molecule, exhibit an enantiotropic SmC mesophase, as evidenced by polarizing optical microscopy and differential scanning calorimetric studies. It has been found that addition of a lateral hydroxyl group along with ester-substitution to the aroylhydrazone core increases the mesomorphic as well as thermal stability of the ligands. Also, the coordination of Ni2+ and Cu2+ with the aroylhydraozone core inhibits the mesomorphic potential of the ligands. A temperature dependent Raman study of one of the members, C12,12LH (m=n=12) has been made to identify phase transitions and to understand the molecular rearrangement as a result of changes in intermolecular interactions at the phase transition. DFT calculations have been performed to obtain the stable electronic structure of the ligand (C6,6LH) and its nickel(II) complex.

Synthesis and Mesomorphic Properties of New Side Chain Liquid Crystalline Oligomers Containing Salicylaldimine Mesogenic Groups

New liquid crystalline salicylaldimine-based homopolymers PLC1 and PLC2 have been synthesized from their corresponding monomers 5-(10-undecenyloxy)-2-[[(4-(hexyloxy)phenyl)imino]methyl]phenol (LC1 ) and 5-(10-undecenyloxy)-2-[[(4-(hexyl)phenyl)imino]methyl]phenol (LC2 ) via free radical polymerization. The polymers were characterized by 1H-NMR, differential scanning calorimetry (DSC) and optical microscopy in polarized light (polarizing microscope). The synthesized polymers have low molecular weights, and so are in the oligomeric domain. The oligomers behave very similarly to their monomers that exhibit smectic mesophases. Replacing the hexyloxy chain by a hexyl chain of the mesogenic unit generates an additional SmC mesophase in the temperature range of both the monomer and oligomer. All the observations suggest that the oligomerization of the liquid crystalline salicylaldimine monomers gives rise to decreased transition temperatures whereas it has no influence on the type and stability of the mesophase formed.

Synthesis, characterisation and mesomorphic properties of a homologous series of oxovanadium(iv) complexes containing a bidentate [N,O] donor Schiff base mesogen

A series of oxovanadium(iv) complexes of the type [VO(L)2], [L = N-(4-n-alkoxysalicylaldimine)-4-hexadecyloxyaniline, n = 8, 10, 12, 14, 16 or 18] have been synthesised and characterised by FT–IR, 1H NMR, 13CNMR, UV–Vis, and FAB mass and magnetic susceptibility measurements. The ligands are coordinated to the vanadyl ion in a bidentate fashion. The mesomorphic behaviour of the ligands and their vanadyl complexes was investigated by polarising optical microscopy and differential scanning calorimetry. The compounds were all highly thermally stable, and their mesomorphic properties were found to depend on the length of the carbon chain. Both the ligands and their higher homologue complexes exhibited a SmC mesophase. In the case of the lower homologues the ligands exhibited the SmC phase but their complexes a SmA mesophase. The mesophase–isotropic transition temperatures for the complexes were significantly higher than those of the ligands. Variable temperature magnetic susceptibility measurements on the vanadyl complexes clearly suggested absence of any exchange interactions among the vanadyl spin centres. Cyclic voltammetry showed a quasi-reversible one-electron response at 0.51 V for the VO(iv)–VO(v) redox couple. Density functional theory studies carried out using DMol3 at the BLYP/DNP level to determine the energy-optimised structure revealed a distorted square pyramidal geometry for the vanadyl complexes, with the alkoxy tails projecting away from one another.

Pyridyl and pyridiniumyl β-diketones as building blocks for palladium(ii) and allyl–palladium(ii) isomers. Multinuclear NMR structural elucidation and liquid crystal behaviour

A series of novel β-diketone ligands bearing alkyloxyphenyl R = C6H4OCnH2n+1 and pyridyl substituents at 1 and 3 positions of the β-diketone core [HLR(n)py] have been prepared and structurally characterized. The corresponding β-diketonate complexes [Pd(κ2-LR(n)py)2] were isolated as a mixture of cis and trans isomers each of them exhibiting the ligand in a NO- or OO-bidentate coordinative mode which were established by multinuclear NMR studies (1H, 13C and 15N). However none of those characteristics were determining to achieve liquid-crystalline properties on the new complexes. By contrast reactions of the aforementioned ligands [HLR(n)py] or those containing the pyridiniumyl substituent [HLR(n)pyH]+ towards the allyl–palladium fragment were successful to afford ionic metallomesogenic materials isolated as PF6 salts of [Pd(η3-C3H5)(κ2-HLR(n)py)][PF6] (I) and [Pd(η3-C3H5)(κ2-LR(n)pyH)][PF6] (II) types. Structural characterization and mesomorphic properties were established by multinuclear NMR and the use of DSC and POM techniques. In complexes I and II the corresponding β-diketone ligands were coordinated as neutral bidentate NO-donor or zwitterionicOO-donor systems, respectively. Complexes of type II exhibit a range of the SmC mesophases significantly greater than that found in the type I.